The product of the present invention is a cable and termination system designed for Adjustable Speed Drives (ASDs, also called Variable Frequency Drives), which system supplies power from a power junction box to an ASD motor control center, as well as providing a low-impedance ground path for common mode (stray) currents generated by ASDs. Due to their high-carrier frequency and smaller pulse rise times, ASDs generate unwanted stray currents that can damage the drive, its motor bearings and insulation, or nearby equipment if those stray currents are not returned properly to the source. The traditional grounding conductor included in ordinary cable is not able to offer a low impedance path for stray currents at high frequencies. Furthermore, asymmetrical phase conduction inherent in ASD designs also requires multiple, geometrically placed grounding conductors (one per phase) for conducting low frequency noise. Internal vibrations of the drive and motor assembly also impact the long-term connection viability of the cable and termination.
The product of the present invention includes cable designs (as detailed below) with alternative termination means. The insulation of the phase conductors within the cable core of the present invention is designed to withstand two to three per-unit transient voltage stress imposed on the cable due to reflected waves of low pulse rise time ASDs. The termination of the present invention is designed for simple, yet effective field installation of the cable to each of the motor control center of the ASD and to the junction box, providing long-term reliability in normal operating conditions.
As hereinafter described, Flexible Tray Cables (TC) constructed and terminated in accordance with the present invention are suitable for existing installations where conduit pre-exists; Metal-Clad Cables (MC) constructed and terminated in accordance with the present invention achieve more consistent lower impedance over a broad spectrum of currents, and are preferred for new installations.